You can do this pne with 2 potrals. Trigger the light that opens the trap door on the floor. Place one portal near the light bridge. Drop into the hole on the floor to the faith plate. After getting shot up in the air put the other portal where you're going to come down. When you go through the portals its quite easy to make it on to the light brdge. The hit the switch turning on the tractor beam & you're done.